The present invention generally relates to a telephone and, more particularly, to long line telephonic noise reduction and to automatic muting apparatus and methods of muting.
A common problem with telephonic communication particularly during conference telephonic calls between multiple locations involving varied communication links, such as radio, communication satellite, under sea cable and local loops, is the generation of audible whistle type noise. This noise is generated most often when there are speaking pauses of the participants of the conference telephone call.
The present inventors have determined that this noise is caused at least in part by acoustical feedback from the telephone speaker to the telephone microphone. This feedback noise problem is particularly acute in the case of so-called speaker telephones, including those built in to desk top computers, video telephones and the like. This is believed by the inventors to be due to several factors. These factors includes the fact that the audio input to the speaker telephone must be of sufficient magnitude to drive a loud speaker that can be heard any where in a room. Also, microphones that are used in speaker telephones have sufficient sensitivity to enable good pickup of sounds anywhere within a room in which the speaker telephone is located while the microphone is acoustically less isolated than in the case of a telephone employing a handset.
Some speaker telephones operate on a simplex basis and automatically mute the speaker telephone microphone during such time speech or other sound above a preselected threshold magnitude is being substantially continuously received and converted to audible sound by the telephonic speaker. During this speaking time, the output signals from the speaker telephone microphone is switched out of circuit, and connection of microphonic output signals to the telephone line is prevented and the communication line is said to be "captured" by the incoming caller. The communication link then remains captured until there is a pause in speaking. Then, when there is a pause, the muting of the microphone is terminated, or unmuted. The microphone is said top be open or on. During the speaking pauses, any party to the conference is enabled to capture the one-way (at a time) communication link. When the local caller starts speaking when the microphone is on the local caller captures the line. Speaking of the local caller, in the case of the other speaker telephones also being simplex, will cause the microphones of the other speaker telephones to be muted until there are pauses in the speaking of the local caller.
Other speaker telephones operate on a duplex basis via a hybrid interface which enables simultaneous two-way conversation. In such duplex speaker telephones, there is no automatic muting of the microphone during speaking of the remote caller and the microphone remains on at all times unless manually turned of by the local caller.